Static RF shimming for parallel-transmit at 7T using the particle-swarm algorithm.

Parallel transmit (pTx) on 7T MRI scanners optimizes the transmit field with optimal RF phases or amplitudes for reduction of specific absorption rate (SAR), or increasing the transmit efficiency by shimming for different brain areas. We used the particle-swarm algorithm to determine optimal RF phases with the acquired transmit field sensitivity maps. Whole-brain transmit field coverage was achieved with the particle-swarm algorithm and high ${{\text{B}}_1}^ + {\text{ - field}}$ efficiency was obtained in regions such as cerebellum or temporal lobes. The SAR levels were decreased up to 33% when included in the optimization process.Clinical Relevance- A fast and robust static RF shimming method allows optimizing transmit efficiency over the whole-brain in a couple of minutes including acquisition and calculation.